SECONDARY EFFECTS IN PIXE ANALYSIS OF BINARY-ALLOYS AND THICK SURFACE-LAYERS

The ratios of intensities of K X-rays of medium elements and L X-rays of heavy elements induced by proton bombardment are particularly sensitive to changes in the geometrical parameters and may be used to determine the thicknesses of surface layers. This intensity ratio of X-rays emitted by the substrate material on those emitted by the surface layer depends sensitively on the thickness of this layer and varies by 2-3 orders of magnitude when the layer thickness increases from 1 to 20 mum. The method is called thick layer PIXE. The effects of the beam size and those of the secondary fluorescence on adjacent materials irradiated with a PIXE microprobe are also discussed. For very narrow beams (1 mum) and high edges in absorption coefficients lor binary targets containing elements with neighbouring atomic weights, the fluorescent yield may be of the same order of magnitude as the primary signals. To illustrate the potentialities of the method, we have measured thicknesses of' gold on copper and nickel on iron. The space apparent resolution of a PIXE microprobe for nickel iron and gold copper binary compounds is also studied. A final example concerns the measurement of diffusion profiles of a nickel layer on an iron substrate treated for temperatures ranging from 450 to 680-degrees-C.